1. Field of the Invention
This invention relates generally to a fiber optic switch, and more particularly concerns a two-by-two fiber optic switch for use in Local Area Network (LAN) applications using an optical fiber dual ring system.
2. Description of the Prior Art
Modern Local Area Networks are experiencing increasing data transmission rates. The electrical signals traditionally used (either digital or analog) in LANs cannot satisfy the increased data transmission rates. Because of this, LANs are increasingly being constructed with optical fiber instead of more traditional electrical cables. Optical fiber cable is ideal for use in LANs because they can carry much larger quantities of data than traditional cable. Also, optical fiber cable does not create the electromagnetic interference (EMI) associated with electrical cable used in a LAN.
These optical fiber cables are connected by fiber optic switches. An optical fiber switch is used to change the optical path to allow transmission of data into the LAN, reception of data by a terminal from the LAN, or allow transmission of data around the LAN and the local (where data is transmitted between a transmission location to a receiving location), respectively.
By switching the optical switch between the inserted state (where data is either inserted or retrieved from the information ring) and bypass state (where data is transmitted inside the information ring), the two-by-two switch can change the optical path in the LAN. Optical signals from the information ring can also be isolated while the continuity of the information ring is maintained.
A de facto industrial standard known as fiber data distributed interface (FDDI) has developed that outlines basic requirements for fiber optic switches.
In optical fiber switches, either multi-mode fiber or single-mode fiber can be used. Regardless of what type of fiber is used, it has always been very difficult to align optical paths when bare fiber is used. Because fiber cores are so small, a misalignment of a few micrometers can cause large insertion losses. This is especially true when using single-mode fiber.
This misalignment problem has been addressed to some extent in the prior art through the use of a Grade Refractive Index (GRIN) lens. The GRIN lens makes the fiber act as if its core diameter has been enlarged to the size of the GRIN lens diameter, thereby making the fiber core diameter behave as if it was at least ten to one-hundred times larger. As a result insertion losses will be minimized when there is a few micrometers of misalignment between the light path from the input fiber to the output fiber. Inherent misalignments cannot be corrected thought the use of a GRIN lens.
Currently, there are two different technologies used to make optical fiber switches (exclusive of the integrated optic switch). A first is known as moving fiber. In this technology either the input optical fibers or the output optical fibers are actually reoriented to switch the light path between outputs. The second is known as moving prism or mirror. in this technology the refractive medium, i.e. the prism, or the mirror is reoriented to switch the light path between outputs while the fibers do not move. These prior art technologies, however, have suffered from slow switching speeds, unacceptable insertion losses and low stability (e.g. alignment problems).
An example of an optical system that uses a moving reflector assembly is disclosed in co-pending application, U.S. Ser. No. 08/028,398, by the same inventor as this application. It is hereby incorporated by reference in its entirety.